Exhaust gas discharged from an internal combustion engine of an automobile or the like contains harmful components such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx), and therefore, it is necessary to purify these components. That is, hydrocarbons (HC) and carbon monoxide (CO) are purified by oxidizing the gases using catalysts, and nitrogen oxides (NOx) needs to be purified through reduction using catalysts.
Three-way catalysts have been traditionally used as catalysts for exhaust gas purification of this kind.
Regarding such three-way catalysts, there are catalysts obtained by arbitrarily combining a noble metal such as Pt, Pd or Rh with alumina, ceria, zirconia or a composite oxide thereof, and applying the combination on a honeycomb carrier formed of a ceramic or a metal. For example, catalysts for exhaust gas purification containing composite oxides having an apatite structure have been proposed (see, for example, Patent Documents 1 and 2).
Furthermore, there have also been proposed catalysts for exhaust gas purification, formed from an AlPO4 compound and at least one noble metal component selected from the group consisting of Pt, Pd and Rh supported on the AlPO4 compound (see, for example, Patent Documents 1, 3 and 4).